An Occultation by Pluto’s Moon Charon?

This is an important update to yesterday's AstroAlert concerning Pluto's very close pass near the 8.7-magnitude star SAO 160793 on Sept. 27, 2007.

David Herald of Canberra, Australia, has updated his earlier prediction of this Pluto-Charon appulse, and it turns out that Pluto's innermost moon, Charon, could actually occult the star. Herald bases his update on a new Pluto ephemeris, corrected using the March 18th Pluto occultation (which was observed from the western USA) and other recent occultations.

Herald's revised prediction shows the southern limit of the occultation by Charon just grazing the Earth over Mongolia and south-central Siberia. With the remaining uncertainties, an occultation by Charon lasting more than 100 seconds is possible between 14:55 and 15:10 Universal Time on September 27th for observers in western China, Mongolia, and southern Siberia. There is also some chance of an occultation a little farther south, from central Asia to southern China, and even possibly northern India. He's sent some maps and charts that I've posted on my website:

Note that my remarks yesterday still apply concerning occultations by possible Plutonian rings.

To recap, the star is also known as BD –16° 4607, P507, and UCAC2 25587116. It is at right ascension 17h 44m 38.4s, declination –16° 46' 35" (equinox 2000.0), and its spectral type is K5.

For other information about this important appulse, check the Massachusetts Institute of Technology's website:

Reporting Your Observations

For occultations of stars by solar-system bodies, the International Occultation Timing Association has special report forms (.xls versions preferred, but plain-text forms are available as well) at these URLs:

Once you complete one of these forms, please send it to IOTA's e-mail address for reporting asteroid-occultation observations:

Final note: If you are reading an e-mail or printed version of this AstroAlert, be sure to go to our online AstroAlerts page and check for possible further updates:

David W. Dunham

Contributing Editor

Sky & Telescope
All comments must follow the Sky & Telescope Terms of Use and will be moderated prior to posting. Please be civil in your comments. Sky & Telescope reserves the right to use the comments we receive, in whole or in part, and to use the commenter’s username, in any medium. See also the Terms of Use and Privacy Policy.